This application relates to apparatus, systems, and techniques for optical communications based on polarization division multiplexing.
Optical communications can be implemented based on spectrally-efficient optical communication techniques to increase capacity of communication systems. Optical wavelength-division multiplexing (WDM), for example, has been widely used to increase the amount of data to be transmitted in a single fiber by simultaneously transmitting multiple optical WDM channels through the fiber. At each WDM wavelength, the state of optical polarization can be used to further increase the bandwidth of information transmission in optical WDM communication lines and systems. For example, information can be encoded in the polarization state through polarization division multiplexing (PDM) schemes for optical transmission. In one implementation PDM, for example, two different data channels can be encoded onto and carried by two different polarizations at the same WDM wavelength. In this and other polarization based data encoding systems, there is a need to mitigate effects of time-dependent polarization rotations in an optical transmission line in order to properly separate two PDM-encoded data channels at an optical receiver.